reduced vcat for more flexibility in arguments

src/groupeddataframe/grouping.jl

@@ -343,18 +343,19 @@ combine(gd::GroupedDataFrame, f::Any) = combine(f, gd)
 # pair syntax  
 function combine(gd::GroupedDataFrame, args::Union{Pair, AbstractVector{<:Pair}}...; kwargs...)
 
-    # todo: fix this bad naming 
+    # handle pairs on their own so we can iterate 
+    args = reduce(vcat, args)
+
+    if args isa Pair
+        args = [args]
+    end
+
     # nams: the name of the new variable 
     # for the keyword arguments, this is explicitely given
     nams_kw = collect(propertynames(values(kwargs)))
     # the pair of input column => function 
     pairs_kw = collect(values(values(kwargs)))
 
-    # handle pairs on their own so we can iterate 
-    if args isa Pair
-        args = [p]
-    end
-
     # For the pairs, we need to auto-generate the names of the new columns here. 
     # i.e. :b => mean gets the name :b_mean
     nams_main = [Symbol(names(gd.parent)[index(gd.parent)[first(p)]],